I 10 FOSSIL ECHIDNAS many other mammals." In &7iidnat too, but not in Ornitho- rhy fichus, the hemispheres are well convoluted, though the arrange- ment of t'hese convolutions cannot be brought into line with what is known concerning the convolutions upon the hemispheres of other mammals. It had been stated that in. these animals, at least in JSeJiidna, there were only two optic lobes, as in lower vertebrates, instead of the mammalian four. The late Sir W. H. Flower set this matter at rest,1 and showed that J&ch-idna was in this respect typically mammalian. The absence of the corpus callos,um is one of the principal features separ- ating the Monotremes from other mammals, The Monotremata are repre- sented to-day by two types, Orn-itho- rliyticfaiis and ItJeJiidnct,, which are no doubt worthy of being placed in separate families, Fossil remains of the group (apart from the prob- lematical Multituberculata) are only known from Pleistocene times in Australia, and consist of the bones of a large species of jEcfoidna, and some fragments of Ornithorhynchus, indicating a smaller animal than tho livinS riatypua Fam. 1. Echidnidae. — This family contains two genera, of which JEchidna is the older and much the better known. The skin is abundantly covered with spines, with which are mingled hairs. The snout is tapering, the tail rudimentary, and the fingers and toes five in number. The spur and gland upon the calcaneum are smaller than in Ornithorhynchus. The claws are very strong, serving to tear open the ants* nests, upon the inhabitants of which the Echidna feeds, licking them, up with a long extensile tongue like that of Myrmecophaga. In relation, to this habit the salivary glands are enormously developed, arid indeed the animal lias been con- founded with MyrmecopJiaga^ as the vernacular name " Australian Anteater " exemplifies, 1 JProc. Zool. jSoc. 1864, p. 18. a MyrmecQpJiaga, aculca+ta, waa the »amo given, bv Shaw.